Oven thermostat with anticipator heater



Dec. 20, 1966 s. B. WELCH OVEN THERMOSTAT WITH ANTICIPATOR HEATER 2Sheets-Sheet 1 Filed June 12, 1964 MULLION 5' ase 1 )8 BROiL TH 5:12 ATTO'RUEIY Dec. 20, 1966 s. a. WELCH OVEN THERMOSTAT WITH ANTICIPATORHEATER 2 Sheets-Sheet 2 Filed June 12, 1964 INVENTORS sTArQLEY B. \DE LCH Fse s ATTO'RMEY United States Patent 3,293,410 OVEN THERMOSTAT WITHANTICIPATOR HEATER Stanley B. Welch, Louisville, Ky., assignor toGeneral Electric Company, a corporation of New York Filed June 12, 1964,Ser. No. 374,680 6 Claims. (Cl. 219-393) The present invention relatesto a domestic oven, and particularly to an oven having a hydraulicthermostatic control system which will operate through two temperatureranges such as the normal cooking range of about 150 F. and 550 F. aswell as in a heat cleaning temperature range having a maximumtemperature somewhere between about 750 F. and 950 F.

Hydraulic oven thermostats have been used for many years, and they havebeen perfected to a high degree of reliability. One such thermostatdesign is disclosed in the patent to W. J. Ettinger No. 2,260,014 datedOctober 21, 1941 and assigned to General Electric Company, the assigneeof the present invention. Such hydraulic thermostats include anelongated bulb or probe formed on the end of a capillary tube, and thistube is in turn joined to a bellows or diaphragm within the thermostathousing. Such a housing is usually mounted on the control panel orbacksplash of the range. The normal oven cooking temperatures havealways been below about 550 F. maximum, and the thermally responsivefluids used in such thermostats have been able to withstand this degreeof. temperature without difliculty. However, the known thermallyresponsive fluids available today cannot be operated at temperature muchabove 650 F.

In recent years a self-cleaning oven design has been perfected whichautomatically cleans the food particles and grease spatterings from theinner walls of the oven cavity to free the housewife of the drudgery ofwashing, scrubbing or scraping the baked-on soil that normallyaccumulates during the normal cooking operations. For a betterunderstanding of the principles of a self-cleaning oven, attention isdirected to Patent No. 3,121,158 of Bohdan Hurko which is also assignedto the General Electric Company, assignee of the present invention.

Heretofore, strong chemical agents have been devised and arecommercially available for the express purpose of removing food soil ofthis type under these conditions. However, even the best of thesecleaning agents require strong rubbing action and a great deal of timeand energy to complete the task satisfactorily. Also, there exists asafety hazard that the chemicals might cause injury to the users handsor eyes if the directions for use are not followed closely.

Once the principle of automatic heat cleaning of domestic ovens by themethod of pyrolysis was perfected many different systems of applying theheat and controlling the cleaning operation were devised to obtain theoptimum results. In order to gain the maximum reliability, standardcomponents were used where possible to take advantage of the years ofengineering development and know-how gained by working with thecomponents. The high temperatures experienced during a heat cleaningoperation within the oven raises a problem as to how to protect thefluid in the hydraulic thermostat so that it remains operational.

The principal object of the present invention is to provide a hydraulicthermostat for a high temperature oven including an external temperaturesensor that is provided with an anticipator heater so as to reduce thetemperature lag between the oven air and the sensor.

A further object of the present invention is to provide a hydraulic oventhermostat with an external temperature sensor or bulb in thermalcontact with the outside of 3,2 93 ,410 Patented Dec. 20, 1966 an ovenliner during normal cooking operation, with means for moving the bulbaway from the oven liner a predetermined amount before a heat cleaningoperation is started so the bulb then senses a temperature which is ananalog of the oven liner temperature and the bulb temperature neverrises above about 550 F.

A further object of the present invention is to provide a hydraulic oventhermostat with an external temperature sensor of the class described inassociation with an air cooled box structure or heat sink for drawingoff heat from the sensor during the heat cleaning operation.

A still further object of the present invention is to provide aself-cleaning oven with a hydraulic thermostat having an externaltemperature sensor provided with an anticipator heater, there being alatching mechanism for a door of the oven and a connection between thelatching mechanism and the temperature sensor so that when the door islatched for the heat cleaning operation the sensor will automatically bewithdrawn from contacting the oven liner.

The present invention, in accordance with one form thereof, isincorporated in a domestic oven that has an oven cavity formed by abox-like oven liner and a frontopening access door. Heating means isprovided for supplying heat energy to the oven cavity both for normalcooking operations as well as for raising the temperature above thenormal cooking temperatures during an automatic heat cleaning cycle. Ahydraulic thermostatic control system is incorporated with the oven tosense the oven temperature and govern the heating means for holding adesired preset temperature within the oven cavity.

The hydraulic thermostat of the present invention includes an externaltemperature sensor or bulb that is located outside the walls of the ovenliner and in heat transfer contact therewith to sense the temperature ofthe oven wall. An anticipator heater is associated with the bulb, andthe heater is energized whenever the said heating means is energized soas to reduce the temperature lag between the oven air and the bulb.Other modifications include means for separating the bulb from the ovenliner prior to the heat cleaning operation so that the bulb temperatureis an analog of the oven wall temperature and never rises above amaximum temperature of about 550 F. If found desirable, an air coolingmeans could be associated with the bulb in its retracted position todraw off heat from the bulb and provide maxi-mum protection.

My invention will be better understood from the following descriptiontaken in conjunction with the accompanying drawings and its scope willbe pointed out in the appended claims.

FIGURE 1 is a left side elevational view of a freestanding electricrange embodying the present invention with parts broken away to show thetop portion of the oven cavity and particularly the location of theexternal temperature sensor of the hydraulic thermostat.

FIGURE 2. is a top cross-sectional plan view of the oven showing a doorlatching mechanism and its connection with the external temperaturesensor or bulb, the view being taken on the line 2-2 of FIGURE 1.

FIGURE 3 is a transverse cross-sectional elevational view at the back ofthe oven showing the bulb in thermal contact with the oven liner and aportion of the connection means between the latching mechanism and thebulb to effect the retraction of the bulb prior to the heat cleaningoperation.

FIGURE 4 is a cross-sectional view similar to that of FIGURE 3 exceptthe bulb is shown in its retracted position away from the oven liner asit would appear during the heat cleaning operation.

FIGURE 5 is a schematic diagram showing the heating means, and circuitcontrol and temperature control means for the oven of the presentinvention.

Turning now to a consideration of the drawings and in particular toFIGURE 1 there is shown for illustrative purposes a free-standingelectric range having a body or cabinet structure with a recessed topcooking surface 11 including a plurality of surface heating elements 12,and oven 13 located beneath the cooktop 11, and a backsplasher 14arranged along the back edge of the cooking surface 11 and including acontrol panel (not shown) on which many of the control components suchas a hydraulic thermostat 24 would be mounted for governing theenergization of the various heating elements of the range. The oven 13,has an oven cavity formed by a box-like oven liner 16 and afront-opening access door 17. The oven includes two standard electricheating elements; namely, a lower bake element (not shown) arranged justabove the bottom wall of the oven liner and an upper broil element 18which is located just under the top wall of the oven liner. Because itis important to have generally uniform temperatures on the walls of theoven liner and door during the heat cleaning operation, an additionalheating element known as a mullion or perimeter heater 20 is assembledaround the front of the oven adjacent the door opening. This mullionheater surrounds the oven liner in such a way that the oven door 17protrudes through the plane of the mullion heater as is clearly shown inthe drawing, FIGURE 1.

' Thermal insulating material 22 such as fiberglass or the likesurrounds the outside of the oven liner for retaining as much of theheat within the oven as is possible for eflicient operations as well asto prevent excessive temperatures on the outer surfaces of the rangebody 10 which might otherwise result in personal injury.

An oven thermostat 24 is located in the control panel or backsplash 14,and it serves as a temperature control means for the energization of theheating means; namely, the bake element 15, the broil element 18, aswell as the mullion heater 20, in the case of the heat cleaningoperation. It is necessary for the thermostat 24 to have a temperaturesensor that is in heat transfer relation with the oven for determiningthe oven temperature and signalling this temperature to the thermostat24 which in turn receives and then acts upon this temperatureinformation and controls the temperature to a degree determined by theadjustable setting of the thermostat. Such a sensor is represented by anelongated copper bulb 25 best shown in FIGURE 2 as being positionedagainst the outer surface of the back wall of the oven liner 16. It isshown as being horizontally disposed adjacent the upper portion of theoven to be near the broil element 18. This bulb 25 is joined to thethermostat 24 by a capillary tube 26 as is conventional in this art. Atemperature-responsive fluid such as phenyl, di-phenyl chloride is usedin the system; but as mentioned previously, it cannot be relied upon attemperatures much above 600 F. because it starts to chemically decomposeand lose its desired properties. Also, the copper bulb 25 and capillarytube 26 begin to soften and oxidize at around 700 F. and this oxidationcan continue for only a short time before the fluid will begin to leakout of the system and thus render the thermostat inoperative. The mostcommon location for the thermostat bulb is within the oven cavity, butsince the present invention is primarily for use with a high temperatureself-cleaning oven, measures must be taken to insure that thetemperature of the bulb never approaches near 600 F. This explains onereason for placing the bulb 25 outside of the oven liner so that ratherthan detecting oven air temperatures as heretofore, it detects the ovenwall temperature.

Ordinarily, the temperature of the thermostat bulb would lag behind theoven air temperature by about 100 F. This is caused by the lag of theoven wall temperature of about 75 F. plus the relatively high thermalmass of the bulb and the high thermal resistance between the bulb andthe oven wall. This characteristic causes a high initial oventemperature overshoot and high amplitude cycling. In addition, thethermal resistance between the bulb and the oven wall is not constantand this results in variations in controlled temperature.

As a solution, I have incorporated an anticipator heater 28 over the tipof the bulb 25 as is best seen in FIGURE 2. This heater 28 may be in theform of an insulated wire wound around the bulb or preferably acommercially available wire-wound resistor, and its use reduces thetemperature lag effect and partially compensates for the variablethermal resistance between the bulb and oven. The heat generated by theanticipator heater 28 causes the temperature of the bulb 25 to lead theoven wall temperature. With high thermal resistance, the temperature ofthe bulb may be effectively raised about F. With low thermal resistancea larger portion of the anticipation heat would flow to the oven walland not be effective in raising the bulb temperature. In order to obtaingood thermal conducting action, a thin copper plate 30 is formedintegral with the bulb for the greater portion of the length of the bulbas for instance, from point 31 to point 32. This plate member 30 ismounted on the side of the bulb to be in full contact with the oven wallso as to obtain generally uniform heat distribution along the bulb. Thisplate member 30 stops short of the tip of the bulb so the anticipatorheater 28 can be threaded over the tip and held in place. During normalcooking operations such as Bake, Broil or Time-Bake the themostat bulb25 is in contact with the oven wall and the anticipator heater 28 isenergized simultaneously with any one of the oven heaters. Thus theanticipator heater 28 adds to the heat from the oven to reduce thetemperature lag between the oven wall and bulb during the operation ofthe thermostat.

The use of the oven thermostat 25 is the same during the heat cleaningoperation except the bulb is moved away from the oven wall apredetermined amount as is best seen in FIGURE 4. Associated with thebulb 25 is a box structure 34 which is slightly longer in length thanthe bulb and it includes a suitable linkage 35 for changing the positionof the bulb 25 as will be better understood hereinafter. While the box34 is associated with the bulb 25 at all times, the bulb is displacedfrom the box during normal cooking operations, as is best seen in FIGURE3. However, for the heat cleaning operation, the bulb is moved away fromthe oven wall and into a recessed channel formation 36 in the nearestwall of the box 34 so that the plate member 30 of the bulb serves as acover plate over the channel formation 36 thereby shielding the bulbwithin the confines of the box. In this position the bulb is not exactlyin the box but it is more in the box than out of it.

The blanket of fiberglass insulation 22 covering the back wall of theoven liner 16 is partially supported by a vertical metal panel 38 whichis spaced inwardly from the back wall 39 of the range body as is bestseen in FIGURE 1. Hence, the space between the back wall 39 and theinsulation guard 38 forms a vertical air channel 40 or wiring space atthe back of the range. As is conventional in self-cleaning ovens, forcedair passes down through this air channel. A fan (not shown) is locatedin the bottom of the range and air is drawn in through the back of thebacksplasher 14 to cool the control components therein. The air passesunder the oven liner to be discharged up the vertical sides of the ovenand out from the range under one or more of the surface heating units12.

The box structure 34 of the thermostat bulb is supported by brackets 41and 42 in an opening in the insulation guard 38 as is best seen inFIGURE 1. It will be noticed that the front half of the box is buried inthe insulation 22, while the back half of the box is located in the pathof the air stream passing downwardly through the air channel 40. The box34 is provided with air vents or louvers 42 in the top and bottom wallsso that the movement of room air therethrough will draw off heat fromthe box and hence from the shielded bulb 25 during the high temperatureheat cleaning cycle.

Means must be provided for retracting the bulb 25 before the heatcleaning operation can begin. Perhaps the most logical arrangement is tojoin the bulb 25 to a door latching mechanism 45 that locks the ovendoor 17 during the heat cleaning operation. Thus, whenever the door islocked the bulb 25 will automatically be withdrawn to its position ofFIGURE 4. This door latching mechanism 45 does not form part of thepresent invention, thus, it is merely illustrated diagrammatically,since it is described and claimed in a co-pending application ofClarence Getman, Seral No. 277,174 which was filed on May 1, 1963, andis assigned to the General Electric Company, the assignee of the presentinvention. The latching mechanism includes a manually operable handlelever 46 which extends through an elongated slot 47 in the front edge ofthe cooktop 11 in a position just above and parallel to the top edge ofthe oven door 17. The handle lever is pivoted about a vertical axis 48and it has an angle of movement of about 60. It also has suitable pinand slot connections (not shown) with a swinging hook member 49 which isnormally recessed within the range body 10, but it is capable ofswinging outwardly for engagement with a suitable keeper (not shown) onthe inner surface of the oven door 17. Pivotally connected to the handlelever 46 is a connecting rod 51 that extends rearwardly over the top ofthe oven, and this rod is capable of a reciprocating movement from itspivotal connection point 52 when the handle lever is moved between itsopen and closed positions.

A push-pull or choke cable 54 is fastened to the rear end of theconnecting rod 51 and it is capable of exerting a pushing and pullingforce by virtue of its wire core 55 covered by a flexible metal sheath56. Naturally the two ends of the sheath must be fixed to a rigidsupport. For example, at the rear end a bracket member 58 is used, andit is supported from the rear wall of the box structure 34. The positionof the wire core 55 is not fixed, but it is capable of sliding withinthe sheath 56 depending upon the movement of the latch mechanism 45. Therear extr'emity of the wire core 55 is connected to one end of a bellcrank lever 60, while the lever is pivoted about its center to thebracket member 58 as at 61. The bell crank lever 60 is pivotallyconnected at its other end 62 to a simple link member 63. The linkmember 63 in turn is pivotally connected to a carrier plate 64 as at thepivot point 65 at the center thereof. This carrier plate has extremities66 and 67 for connection to the bulb and plate assembly 25 and 30,respectively. Wire clip members 68 are formed integral with the backside of the plate member 30, and these clip members are engaged by theextremities 66 and 67 of the carrier plate 64 as is best seen in FIGURES2 and 3.

A certain amount of spring bias or snap action is exerted by means of anover-center mechanism 70 which comprises a double assembly, one adjacenteach end of the carrier plate 64 as is best seen in FIGURE 2. Eachassembly comprises a large U-shaped spring member 71 with a base 72 andtwo spring arms 73. The base 72 is fastened to the inner surface of awall of the box 34, while its two spring arms 73 straddle the carrierplate 64. A pair of opposing push rods 74 and 75, representing in unisonan over-center spring device, are each wedged between the carrier plate64 and the distal end of the adjacent spring arm 73. The innermost endof each push rod 74 and 75 extends through a small opening in thecarrier plate 64. Thus, the natural tendency of the U-shaped member 70to maintain generally parallel spring arms 73 is thwarted by thepresence of the push rods 74 and 75. However, this spring tendency isenough to exert a reaction force on the carrier plate 64 so the platemember 30 is always held by a spring force in either one of its extremepositions such as the position in FIGURE 3 against the oven Wall, andthe position of FIGURE 4 against the wall of the box 34.

Turning now briefly to a consideration of the circuit diagram of FIGURE5, the electric range of the present invention is provided'with astandard electrical service of three-wire Edison source of power;nominally of 240 volts, single phase, 60 cycle, A.C. which is usuallyavailable in the average residence having adequate wiring. This voltagesource has a pair of line wires L1 and L2 and a grounded neutralconductor N for supplying an oven selector switch that controls theelectrical load characterized by the three heating elements; namely, thebake element (unnumbered), the broil element 18, and the mullion orperimeter heater 20. The hydraulic thermostat 24 is a double polethermostat having switch contacts 81 and 82 for breaking both sides ofthe line L1 and L2 bringing power to the selector switch 80. The ovenselector switch 80 is shown with a plurality of switch contacts andthese are labeled with designations of specific operations such as Bake,Broil, Time-Bake and Clean. The contacts labeled All are common switchcontacts which are closed whenever the switch is in an energizedposition. The anticipator heater 28 that is mounted on the tip of thebulb 25 is shown connected across line L1 and Neutral whenever thecommon switch contact labeled All is closed and the thermostat contacts81 are closed. During a baking operation the bake element and broilelement 18 are connected in parallel across lines L1 and L2 at 240volts.

During a broiling operation the broil element 18 is the only elementthat is energized and it is connected across line L1 and Neutral at 120volts.

Next is the heat cleaning operation where the bake element and mullionheater 20 are connected in series across lines L1 and L2, while thebroil element 18 is connected in parallel with the series connection ofthe bake and mullion heater across lines L1 and L2. A suitable pilotlight 84 is connected across lines L1 and Neutral whenever the ovenselector switch 80 is energized. Moreover, there is an oven indicatorlight 85 that is energized only when the thermostat contacts 81 and 82are closed during a heating cycle.

Modifications of this invention will occur to those skilled in this arttherefore it is to be understood that this invention is not limited tothe particular embodiments disclosed but that it is intended to coverall modifications which are within the true spirit and scope of thisinvention as claimed.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A domestic oven comprising a cabinet having walls defining an ovencavity, heating means for said cavity, control means for said heatingmeans to etfect various cooking operations, a hydraulic temperaturecontrol means for said heating means settable to control the heatingmeans to hold a selected temperature, said temperature control meanscomprising an elongated fluidfilled bulb having a capillary tube joinedto a temperature responder, said bulb being located outside the walls ofthe oven cavity, and normally in heat transfer relation therewith tosense the temperature of the oven wall, an anticipat-or heaterassociated with the bulb, and means controlling said heater to beenergized when the said heating means is energized so as to reduce thetemperature lag between the oven Wall and the bulb.

2. An electric oven comprising a box-like oven liner and an access doorthat form an oven cooking cavity, heating means for said cavityincluding an upper broil heating element and a lower bake heatingelement, circuit control means for said heating means to efiect variouscooking operations, a hydraulic thermostatic control means for thecircuit control means to control the heating elements for holdingselected temperatures, said thermostatic control means including anelongated fluid-filled 7 bulb located outside and in heat transferrelation with a wall of the oven liner near one of the heating elements,and an anticipator heater assembled with the bulb and connected to beenergized whenever any one of the said heating elements is energized toreduce the temperature lag between the Wall and the bulb.

3. A cooking apparatus comprising a box-like oven liner and an accessdoor that form an oven cooking cavity, heating means for said cavity,control means for said heating means selectably operable to control theheating means to efiect either a bake operation or a broil operation, atemperature control means for said heating means settable to control theheating means when in a bake operation to hold selected bakingtemperatures within the baking temperature range and to control theheating means when in a broil operation at a predetermined boilingtemperature, said temperature control means including a hydraulicthermostat with an elongated fluid-filled bulb located against theoutside of a rear wall of the oven liner, and an anticipator heatercarried by the bulb, said heater being energized Whenever the saidheating means is operated so as to reduce the temperature lag betweenthe rear wall and the bulb.

4. A cooking apparatus comprising a box-like oven liner and an accessdoor that form an oven cooking cavity, heating means for said cavity,control means for said heating means selectably operable to control theheating means to effect either a bake operation, a broil operation or ahigh temperature heat cleaning operation, the bake and broil operationsbeing within a temperature range between about 150 F. and 550 F. Whilethe heat cleaning operation having a maximum temperature somewherebetween 750 F. and 950 F., a temperature control means for said heatingmeans settable to control the heating means for normal cookingoperations as Well as for the heat cleaning operation, said temperaturecontrol means including a hydraulic thermostat with an elongatedfluid-filled temperature sensing bulb located against the outside of awall of the oven liner, and an anticipator heater carried by the bulband energized whenever the said heating means is operated so as toreduce the temperature lag between the oven liner and the bulb, andmeans for moving the bulb away from contact with the oven liner apredetermined amount before the heat cleaning operation is started sothe bulb senses a temperature which is an analog of the oven linertemperature and which bulb temperature never rises above about 550 F.while the liner temperature rises to within the heat cleaningtemperature range of 750 F. and 950 F.

5. An electric oven comprising a box-like oven liner and an access doorthat form an oven cooking cavity,

heating means for said cavity includingan upper broil heating elementand a lower bake heating element, circuit control means selectablyoperable to control the heating elements to effect either a bakingoperation, a broiling operation or a high temperature heat cleaningoperation, the baking and broiling operations being within a normalcooking temperature range between about F. and 550 F., While the heatcleaning operation has a maximum temperature somewhere between about 750F. and 950 F., a temperature control means for said heating elementsettable to control the elements for normal cooking operations as wellas for the heat cleaning operation, said temperature control meansincluding a hydraulic thermostat having a temperature sensing bulbpositioned against an outer surface of the oven liner, and ananticipator heater carried by the bulb and energized whenever theheating element is energized so as to reduce the temperature lag betweenthe oven liner and the bulb, the bulb being in good thermal contact withthe oven liner for obtaining accurate results, and means for moving thebulb away from the oven liner a predetermined amount for the heatcleaning operation so the bulb senses a relatively low temperature whichis an analog of the oven liner temperature, and latching means for theoven door for use during the heat cleaning operation, and connectingmeans between the door latching means and the thermostat bulb so thatwhen the latching mechanism is closed the thermostat bulb will move awayfrom the oven liner.

6. An electric oven as recited in claim 5 wherein the thermostat bulb isprovided with a plate'member of high thermal conductivity integraltherewith and extending for substantially the length of the bulb, saidplate member being on the side of the bulb that engages the oven liner,the said anticipator heater being mounted onto the tip of the bulb, thesaid bulb being associated with a box member, the bulb during normalcooking being in thermal contact with the oven liner, while during theheat cleaning operation the bulb is in thermal contact with the boxmember, an air cooling means for the box member for Withdrawing heatfrom the box and hence from the bulb during the heat cleaning operation.

References Cited by the Examiner UNITED STATES PATENTS 3,121,158 2/1964Hurko 219397 3,176,118 3/1965 Scott 219394 RICHARD M. WOOD, PrimaryExaminer. C. L. ALBRITTON, Assistant Examiner.

1. A DOMESTIC OVEN COMPRISING A CABINET HAVING WALLS DEFINING AN OVENCAVITY, HEATING MEANS FOR SAID CAVITY CONTROL MEANS FOR SAID HEATINGMEANS TO EFFECT VARIOUS COOKING OPERATIONS, A HYDRAULIC TEMPERATURECONTROL MEANS FOR SAID HEATING MEANS SETTABLE TO CONTROL THE HEATINGMEANS TO HOLD A SELECTED TEMPERATURE, SAID TEMPERATURE CONTROL MEANSCOMPRISING AN ELONGATED FLUIDFILLED BULB HAVING A CAPILLARY TUBE JOINEDTO A TEMPERATURE RESPONDER, SAID BULB BEING LOCATED OUTSIDE THE WALLS OFTHE OVEN CAVITY, AND NORMALLY IN HEAT TRANSFER RELATION THEREWITH TOSENSE THE TEMPERATURE OF THE OVEN WALL, AN ANTICIPATOR HEATER ASSOCIATEDWITH THE BULB, AND MEANS CONTROLLING SAID HEATER TO BE ENERGIZED WHENTHE SAID HEATING MEANS IS ENERGIZED SO AS TO REDUCE THE TEMPERATUE LAGBETWEEN THE OVEN WALL AND THE BULB.